Propellant powder and process of making the same



Patented June 14, 1932 UNITED STATES PATENT OFFICE WILLIAM E. WAGNER, OF ALTON, ILLINOIS, ASSIGNOR TO WESTERN CARTRIDGE COM- PANY, OF EAST ALTON, ILLINOIS, A CORPORATION OF DELAWARE PROPELLANT POWDER AND PROCESS OF MAKING THE SAME No Drawing. Application filed May 1,

This invention relates t propellant powders and more particularly to nitro-cellulosenitro-glycerin powders which are progressive burning and adapted particularly for shot shells.

A progressive burning powder should have such characteristics as to cause a slow generation of gas during its initial stages of burning in order to start the projectile into motion gradually; for a fast generation of gas before the projectile has moved any appreciable distance will result in high pressures due to the confined space in which the gas must be accommodated. As the projectile moves along the barrel of the gun and increases in'velocity, the effective volume of the powder chamber is increased so rapidly that gas is not evolved at a rate sufiiciently high to maintain a uniformpressure beyond the point at which the maximum pressure occurs. It is desirable that the initial pressure be limited while the pressure along the gun barrel should be maintained. In order to maintain the pressure along the gun barrel, the core of the grain should be as fast burning as possible.

Gelatinized nitro-cellulose powders, as now made with non-explosive solvents for nitrocelluose, have the disadvantage of presenting an interior of solid texture, which is not sufficiently fast-burning to maintain a desirable pressure for an extended distance along the gun barrel. On the other hand, unge latinized nitro-cellulose evolves gas too rapid- 1y during the ignition and initial stage of combustion and, since it is porous and hygroscopic, is afiected by variations in moisture conditions which render its actions uncertain and hard to control from a ballistic standpoint. WVhile the treatment of ungelatinizod grains with a solvent to gelatinize the surfaces of the individual grains will reduce the penetration of moisture into the body of the fibers, it is found that if the solvent so used is one which leaves the powder grains during drying treatment and in storage the gelatinization in itself is not suflicient to greatly reduce the hygroscopicity of the treated powder grains. On the other hand, if solvents are used whose vapor pressure is 1929. Serial No. 359,708.

sufiiciently'low to remain indefinitely in the powder grains, the amount which it is necessary to' add to give the desired protection against moisture will be sufficient to so reduce the burning rate as to make the powder unsuitable for many purposes, unless the solvent so used for gelatinizing the fibers be nitroglycerin or a similar material which is in itself an explosive.

Any method of merely gelatinizing the fibers of powder grains of open fibrous structure does not materially alter thephysical form and still leaves a porous interior which, by reason of the great amount of burning surface exposed, evolves gas during the initial stage of combustion at too fast a rate to ob tain the desired ballistics for many commercial purposes. A method which has been proposed of introducing a solution of a low nitrogen content intro-cellulose in a volatile solvent such as alcohol through the pores of the grain and then evaporating the solvent is open to the objection that low nitrogen nitrocellulose is more hygroscopic than the higher nitrogen nitro-cellulose and the hygroscopic characteristics of the grains are impaired rather than improved. That method does not allow the use of a high nitrogen cellulose coating, as the kind of solvent necessary to put a high nitrogen nitro-ccllulose into solution would also dissolve the nitro-cellulose of the grains being treated, causing them to adhere one to the other.

In my application Serial No. 359,707, executed and filed of even date herewith, the disadvantages of the prior process have been overcome in that the grains are waterproofed while the fast-burning characteristic, especially of the interior 0 the grain, is retained. In accordance with that process, ungelatin- 'ized nitro-cellulose grains are treated or impregnated with nitro-glycerin in a solvent which is a non-solvent for nitro-cellulose; accordingly, the grain fibers are only surfacegelatinized. The impregnation of a colloided nitro-cellulose grain with intro-glycerin re sults in a faster and more powerful explosive than the untreated powder; but when nitroglycerin is introduced as a gelatinizer into porous grains of uncolloided nitro-cellulose it increases the densitv of the powder grains,

. surface and reduced burning rate of a potentially more powerful explosive results in a grain having a slower rate of gas evolution and consequently in lower gun pressures than with untreated grains. While this is satisfactory for certain purposes, it\ is desirable in many cases to still further reduce the rate of combustion. It is also desirable in some cases to form a harder coating on the powder grains than is attainable when ungelatinized nitro-cellulose grains are treated with a solution of nitroglycerin in a non-solvent for nitro-cellulose. 1

One of the objects of this invention, therefore, is to provide a propellant powder in which the fast-burning interior of the nitrocellulose grain is maintained while this grain is surface-treated, i. e. impregnated or coated so as to waterproof the same; this coating, however, being of such character as to be readily ignitable, but less subject to changes due to varying conditions of humidity than the nitro-cellulose forming the untreated powder grains.

Further objects will appear from the detail description, in which will be described a number of illustrated embodiments it is to be understood, however, that this invention is susceptible of various embodiments other than those described.

In accordance with one embodiment of this invention, ungelatinized nitro-cellulose of the desired degree of nitration is dissolved in a suitable solvent, such as ethyl acetate. To this is then added sufficient of a non-solvent, such as benzol, to start precipitating the nitrocellulose. A slight addition of the solvent brings the precipitate back into solution. Nitro-ccllulose grains can now be treated with the solution, so as to coat the same. The vehicle can now be evaporated in any suitable manner. This provides a nitro-cellulose grain having a coating of nitro-cellulose; however, the grains are not colloided at their surfaces, while the degree of penetration may be controlled by the viscosity of the solution with respect to the character of the grain, having regard to porosity.

In accordance with another embodiment of this invention, the nitro-cellulose solution, with a non-solvent added to nearly precipitate, has added thereto nitro-glycerin in th required proportion. The addition of the nitro-glycerin will not greatly change the precipitation point; for the addition ofnitroglycerin does not greatly change the proportion of non-solvent to be added; however, the

proportions of the solvent and non-solvent can readily be so made that, with the addition of nitro-glycerin, there is no excess of active solvent for nitro-cellulose which may attack the nitro-cellulose powder grains being treated and cause them to stick together. It will be noted that where benzol is used, it being a solvent-for nitro-glycerin, a'solution of nitro-cellulose and nitro-glycerin is formed with the nitro-cellulose near the precipitating point, and the grain can, therefore, be coated therewith, thevehicle composed of the solvent and non-solvent being evaporated in any suitable manner, so as to leave a coating whose impregnation is determined by the viscosity of the solution with respect to the characteristics of the grain.

A detailed description of an illustrated em- 4 bodiment of this invention will now be given, the procedure being as follows:

A. 10 parts of one-half second gun cotton is dissolved in 59 parts of ethyl acetate, to which is added 31 parts of benzol to form a solution.

B. .A 40% solution of benzol is prepared.

C. 30 parts of the A solution is mixed with parts of theB solution.

nitro-glycerin in D. To 93 parts of the C solution is added 7 parts of diamyl-phthalate.

E. 100 parts of uncolloided nitro-cellulose powder grains of the desired granulation are treated with from 100 to 200 parts of the D solution in order to coat the same. The coating is applied by spraying, enough time being taken to apply the desired thickness of coat, so as to insure an even distribution on all the grains. The coating can, however, be applied in a rotating barrel or similar device by adding the desired amount of the solution to the powder and mixing the two together, then keeping the mass in motion while the volatile solvent and non-solvent evaporate. If the solvents and non-solvents are miscible with water, the coated grains may be water dried to remove all but traces of solvents and non-solvents if it is desirable to do so. However, solvents and'non-solvents such as ethyl acetate and benzol evaporate I readily even at ordinary temperature, but if desired, the time necessary to remove them can be decreased by raising the temperature to 50 or 60 I The rate of evolution of gas to suit the weight of the projectile charge, the resistance of crimp of the cartridge case, as well as the resistance in the gun bore, can be controlled by the granulation of the nitro-cellulose powder, and by the thickness and proper proportioning of the nitro-cellulose coating. It is possible by this method of treatment to reduce the rate of evolution of gas during the initial stage of combustion so that the inertia and resistance of the projectile will be overcome slowly and without shock at low breach pressures followed by a fast evolution the barrel. Moreover, an allowable pressure can be maintained a greater distance along the gun barrel than is possible with powder grains not so treated. The. initial combustion can, moreover. be deterred by depositing a coating of nitro-cellulose over the grain which has been previously coated with nit-ro cellulose and intro-glycerin. In this case, nitro-cellulose of any suitable degree of nitration is dissolved in a suitable solvent and the grain treated with the solution the procedure of adding a non-solvent to bring the solution to a precipitating point can again be resorted to. In accordance with arotber embodiment of this invention, the solution containing the intro-cellulose and nitro-glycerin can have incorporated therewith a suitable deterrent, such as diamyl-phthalate. dihutyl-phthalate, tri-cresyl-phosphate, etc., before application of the same to the powder grains. These deterrents further perform the function of plasticizers to prevent cracking of the coating upon drying.

It will thus be seen that the invention accomplishes its objects. A grain is produced in which the fast-burning porous interior of nitro-cellulose is retained. while the coating prevents penetration of air and moisture to the interior of' the grain. The coating is tough and dense, as well as hard and homogeneous and without crevices or cracks. While the surface of the grain is slower burning than the interior. it is readily ignitable and. in fact. characterized by ease of ignition. However, the initial rate of burning can be retarded as heretofore described, so as to control the initial rate of burning and the initial pressure; while. on account of the fastburning characteristic of the interior, the pressure will be maintained for an extended distance along the gun barrel. as is desired. The presence of the nitro-cellulose in the coating not only has the effect of slowing down the initial combustion, but of securing a hard,

- dense and homogeneous coating. free from cracks. and. therefore, providing an effective waterproofing.

If a porous grain is being treated and it is desired to maintain a very porous fast-burning interior. the viscosity of the solution should be adjusted by selecting nitro-cotton of the proper degree of nitration, so that the solution will not be thin enough to penetrate the body of the grain to any extent. If it is. however. desired to partly fill the voids between the nitro-cellulose fibers. so as to coat the individual fibers. then a more sol uble nitro-cotton can be selected. so as to give the desired viscosity. In this way. the characteristics of the grain-can be controlled.

While this invention is applicable to the treatment of nitro-cellulose grains generally, it is particularly applicable to the treatment of uncolloided fibrous grains of open texture. The grain may comprise nitro-cellulose prepared from any suitable form of cellulose, such as cellulose from cotton, wood, straw, etc. While nitro-glycerin is particularly applicable, in connection with n1trocellulose and its derivatives, for waterproofing or coating the grains, nitrates of polyglycerin or ethylene-glycol; or other suitable nitrates of glycerin may be employed. It will, therefore, be understood that the terms nitro-cellulose and nitro-glycerin are used descriptively and not limitatively. It will, furthermore, be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations; that is contemplated by and is within the scope of the appended claims. hile the propellant described is particularly useful for shot Shells, some of the features of this invention are applicable to propellants generally. It is, furthermore, to be understood that various changes may be made in details and operations, within the scope of the appended claims, without departing from the spirit of this invention. It is. therefore, to be understood that this invention is not to be limited to the specific details and operations described.

Having thus described the invention what is claimed is:

1. In the art of making propellant powders, the process comprising, treating nitrocellulose grains with a solution containing intro-cellulose near its precipitating point.

2. In the art of making propellant powders, the process comprising, treating nitrocellulose grains with a volatile solution containing nitro-cellulose near its precipitating point and evaporating the vehicle.

3. In the art of making propellant powders, the process comprising, treating nitrocellulose grains with a solution containing nitrocellulose and nitro-glycerine.

4. In the art of making propellant powders, the process comprising, treating nitrocellulose grains with a solution containing a volatile vehicle, nitro-cellulose and nitroglycerine and evaporating the vehicle.

5. In the art of making propellant powders, the process comprising, treating nitrocellulose grains with a solution containing intro-cellulose and nitro-glycerine near the precipitating point of the nitro-cellulose.

6. In the art of making propellant powders, the process comprising, treating nitrocellulose grains with a solution containing a volatile vehicle, nitro-cellulose and nitro-. glycerine near the precipitating point of the nitro-cellulose and evaporating the vehicle.

7. In the art of making propellant powders, the process comprising, treating nitrocellulose grains Wth a solution containing nitro-cellulose and nitro-glycerine and treating the grains with a intro-cellulose solution.

8. In the art of making propellant powrent.

ders, the process comprising, treating nitrocellulose grains with a solution contalmng n'itro-cellulose, nitro-glycerine and a deter- 9. In the art of making propellant powders, the process comprising, treating nitrocellulose grains with *a solution containing nitro-cellulose and nitro-glycerine and adjusting the viscosity of the solution to control its penetration.

10. In the art of making propellant powders, the process comprising, preparin a solution of nitro-cellulose, adding su cient non-solvent to nearly precipitate the nitrocellulose and treating nitro-cellulose grains with the solution.

11. In the art of making propellant powders, the process comprising, preparing a so lution of nitrocellulose and nitro-glycerine, adding suflicient non-solvent for nitro-cellulose to nearly precipitate the same and treating nitro-cellulose grains with the solution.

12. In the art of making propellant ders, the process comprising, treating nitrocellulose grains with a solution containing nitro-cellulose, nitro-glycerine and a deterrent, while thesolution is near the precipitating point of the nitro-cellulose.

13. In the art of making propellant powders, the process comprising, preparing a solution of nitro-cellulose and nitro-glycerine by the employment of a nitro-cellulose solvent and sufiicient of a nitro-glycerine solvent which is a non-solvent for nitro-cellulose to nearly precipitate the nitro-cellulose and treating nitro-cellulose grains with the solution.

14. In the art of making propellant powders, the process comprising, preparing a solution of nitro-cellulose, .adding sufficient non-solvent to nearly precipitate the nitrocellulose, adding thereto a nitro-glycerine solution and treating nitro-cellulose grains v with the solution.

15. In the art of making propellant powders, the process comprising, preparing a solution of nitro-cellulose and nitro-glycerine, adding sufficient non-solvent for nltro-cellulose to nearly precipitate the nitro-cellulose and treating nitro-cellulose grains with the solution.

16. A propellant powder grain of nitrocellulose surface-treated with nitro-cellulose and nitro-glycerine.

17. A propellant powder grain of nitrocellulose surface treated with nitro-cellulose, nitro-glycerine and a deterrent.

In testimony whereof, I afiix my signature this 12th day of April 1929.

WILLIAM E. WAGNER. 

